1. Technical Field
The present invention relates to a printing apparatus, and a printing method.
2. Description of Background Art
An image forming apparatus, in which an image formed on an intermediate transfer rotating medium is transferred to a recording medium to achieve printing (see, for example, JP-A-2007-112117), is known. In the configuration disclosed in JP-A-2007-112117, an image is formed on an intermediate transfer rotating medium with a UV curable ink having predetermined spectral absorption properties, and the ink is brought to a partially cured state by irradiation of a UV light of a predetermined wavelength. The image formed by the partially cured ink on the intermediate transfer rotating medium is then transferred to a recording medium. After the transfer, the ink is permanently cured by irradiation of the UV light of a predetermined wavelength.
However, the image transfer by such a method requires, for example, accurately controlling the intensity and the duration of the UV irradiation to adequately bring the ink to the partially cured state before the transfer. Another possible drawback is that the spectral absorption properties of the ink, depending on its relationship with the irradiation wavelength of the UV light used, might limit the irradiation conditions of the partially cured ink, or might pose difficulties in adequately bringing the ink to the partially cured state. Depending on the irradiation wavelength of the UV light, it might be also difficult to use inks other than UV curable inks of specific spectral absorption properties.
In partial curing of UV curable ink dots by UV irradiation, the curing will proceed faster on the dot surface than inside the dot because the surface is directly exposed to the UV light. For example, partial curing to make the inside of the ink dots suitable for transfer may overcure the ink dot surface. The overcuring of the ink dot surface may lower the adhesion of the dot surface, and the ink may not be properly transferred to a medium. Conversely, the ink dots may not be sufficiently cured inside by partial curing to make the ink dot surface suitable for transfer. In the transfer step, for example, the ink may remain in a partially liquid state when the inside of the ink dots is insufficiently cured, and ink separation may occur in the liquid portion of the ink. This may result in ink transfer failure, or may cause ink bleeding after the transfer.